By moving a magnet close to and then away from a magnetically activated switch, the switch can be toggled between opened and closed positions. The distances between the magnet and the magnetically activated switch required to open and close the switch are a function of the strength of the magnet and the sensitivity of the switch.
A magnetically activated switch can be used in a sensing environment. One application is a gas metering device that uses a magnetic reed switch to sense the rotations of a rotating device within a gas meter. For example, as shown in FIG. 1, to sense the rotations of a rotating device, a magnet 140 could be fixed onto the rotating device (not shown) or the magnet 140 could be fixed to a disk 155 in direct or indirect contact with, and therefore rotating at the same rotational velocity as, the rotating device within the gas meter. The magnet 140 and magnetic reed switch or switches 165, 170 can be positioned so that the magnet 140 rotates close enough to the magnetic reed switches 165, 170 to toggle a switch closed and then opened as the magnet 140 rotates over and then away from the switch. A logic circuit activated by the opening and closing of the switches can be used to increment a counter for each rotation sensed by a switch.
A rotation sensing device as described above can be restrained in size, depending on the application. If the size is restrained, the strength of the magnet and the sensitivity of the switch or switches must be carefully selected, or else a switch may remain in the closed position when the magnet has rotated away from the switch or the switch may fail to close when the magnet passes through the activation position.